I know you are joking, but there is plenty of water in the Atacama: rivers that originate in the Andes [wikipedia.org]. They either flow out in the sea (through canyons), in salt pans, or sometimes through a tube to the coastal towns.

The Atacama is pretty inhospitable, especially for people trying to run these tests. They could recreate the conditions in a large indoor lab easily enough. All you need is rocks, sand, fans, and some dehumidifiers. I don't really get why they need to go to the Atacama.

I wonder what the price tag is to fill a large indoor space with enough sand for a good test. Don't forget we also need to pay for damage to the building from blowing sand everywhere and heating it up to uncomfortable temperatures. Then there's the price to clean it all back out for the next project.

"They" are many different teams in many different places around the world, so they'll almost all be traveling anyway. Dumping a pile of sand in a building is just an unnecessary expense for no real benefit.

Fill a building in California with sand and it's rapidly going to be full of microorganisms, even if you bake the dirt first. They fed dirt from the Atacama to the Viking lander that was kept on Earth, and it didn't find life.

Fill a building with rocks and sand and it's all fluffy and aerated. Ground textures are nothing like real-world terrain. Hills can only be a few meters tall and steep slopes are very difficult to build without additives.

No it isn't. Atacama desert has considerable amount of wild life, mine workers and tourists. I've been there as a back packer, and you can live there for a few weeks without problems in a shoestring budget.